Anne H. Clites

Temporal and Spatial Variability of Great Lakes Ice Cover, 1973–2010*

AbstractIn this study, temporal and spatial variability of ice cover in the Great Lakes are investigated using historical satellite measurements from 1973 to 2010. The seasonal cycle of ice cover was constructed for all the lakes, including Lake St. Clair. A unique feature found in the seasonal cycle is that the standard deviations (i.e., variability) of ice cover are larger than the climatological means for each lake. This indicates that Great Lakes ice cover experiences large variability in response to predominant natural climate forcing and has poor predictability. Spectral analysis shows that lake ice has both quasi-decadal and interannual periodicities of ~8 and ~4 yr. There was a significant downward trend in ice coverage from 1973 to the present for all of the lakes, with Lake Ontario having the largest, and Lakes Erie and St. Clair having the smallest. The translated total loss in lake ice over the entire 38-yr record varies from 37% in Lake St. Clair (least) to 88% in Lake Ontario (most). The tot...

Interannual variability of Great Lakes ice cover and its relationship to NAO and ENSO

[1] The impacts of North Atlantic Oscillation (NAO) and El Nino–Southern Oscillation (ENSO) on Great Lakes ice cover were investigated using lake ice observations for winters 1963–2010 and National Centers for Environmental Prediction reanalysis data. It is found that both NAO and ENSO have impacts on Great Lakes ice cover. The Great Lakes tend to have lower (higher) ice cover during the positive (negative) NAO. El Nino events are often associated with lower ice cover. The influence of La Nina on Great Lakes ice cover is intensity-dependent: strong (weak ) La Nina events are often associated with lower (higher) ice cover. The interference of impacts of ENSO and NAO complicates the relationship between ice cover and either of them. The nonlinear effects of ENSO on Great Lakes ice cover are important in addition to NAO effects. The correlation coefficient between the quadratic Nino3.4 index and ice cover (� 0.48) becomes significant at the 99% confidence level. The nonlinear response of Great Lakes ice cover to ENSO is mainly due to the phase shift of the teleconnection patterns during the opposite phases of ENSO. Multiple-variable nonlinear regression models were developed for ice coverage. Using the quadratic Nino3.4 index instead of the index itself can significantly improve the prediction of Great Lakes ice cover (the correlation between the modeled and observed increases from 0.35 to 0.51). Including the interactive term

Accuracy of trajectory calculation in a finite-difference circulation model

Abstract The prediction of drifting object motion due to currents in an irregular body is a complex problem with a wide range of practical applications. Simple numerical methods for interpolating current velocity fields have spatial interpolation and time integration errors that result in misleading solutions. The method described in this paper minimizes these problems, yielding much more accurate predictions. This method can be easily implemented in other finite-difference models or finite-element models.

Development of the Great Lakes Ice-Circulation Model (GLIM): Application to Lake Erie in 2003–2004

ABSTRACT To simulate ice and water circulation in Lake Erie over a yearly cycle, a Great Lakes Ice-circulation Model (GLIM) was developed by applying a Coupled Ice-Ocean Model (CIOM) with a 2-km resolution grid. The hourly surface wind stress and thermodynamic forcings for input into the GLIM are derived from meteorological measurements interpolated onto the 2-km model grids. The seasonal cycles for ice concentration, thickness, velocity, and other variables are well reproduced in the 2003/04 ice season. Satellite measurements of ice cover were used to validate GLIM with a mean bias deviation (MBD) of 7.4%. The seasonal cycle for lake surface temperature is well reproduced in comparison to the satellite measurements with a MBD of 1.5%. Additional sensitivity experiments further confirm the important impacts of ice cover on lake water temperature and water level variations. Furthermore, a period including an extreme cooling (due to a cold air outbreak) and an extreme warming event in February 2004 was examined to test GLIMs response to rapidly-changing synoptic forcing.

The History of Lake Superior Regulation: Implications for the Future

Abstract Lake Superior outflows have been regulated for the past 80 years. The last 15 years have encompassed both extremely high water supplies and lake levels and subsequent drastic declines in the levels of Lakes Superior and the lower lakes. The IJC is considering a study whose purpose would be the reexamination of the current Lake Superior regulation plan, which has been in use since 1990. In preparation for that discussion, several different aspects of past and potential future Lake Superior levels were analyzed. The stage-discharge equation representing natural flow conditions for the pre-1900 Lake Superior outlet was used to simulate “unregulated” Lake Superior outlet conditions, using actual water supplies. Net basin supplies developed for a climate change study were used to evaluate the potential effects of regulation on future levels. A 50,000 year set of stochastic net basin supplies, based upon the present climate, was also used to provide hypothetical upper and lower bounds. By comparing recorded Lake Superior levels to what might have happened in the absence of regulation and what may occur with future supplies, it is hoped that the development and/or evaluation of any future adjustments to the regulation criteria for Lake Superior might be aided.

Satellite-Tracked Current Drifters in Lake Michigan☆

Abstract Satellite-tracked current drifters are being used to monitor near-surface currents in Lake Michigan. These drifters are now commercially available, and preliminary tests show their satellite-determined positions to be within 0.5 km. The drifters appear to be ideal for monitoring near-surface lake currents and testing hydrodynamic lake models.

A record-breaking low ice cover over the Great Lakes during winter 2011/2012: combined effects of a strong positive NAO and La Niña

Abstract A record-breaking low ice cover occurred in the North American Great Lakes during winter 2011/2012, in conjunction with a strong positive Arctic Oscillation/North Atlantic Oscillation (+AO/NAO) and a La Niña event. Large-scale atmosphere circulation in the Pacific/North America (PNA) region reflected a combined signal of La Niña and +NAO. Surface heat flux analysis shows that sensible heat flux contributed most to the net surface heat flux anomaly. Surface air temperature is the dominant factor governing the interannual variability of Great Lakes ice cover. Neither La Niña nor +NAO alone can be responsible for the extreme warmth; the typical mid-latitude response to La Niña events is a negative PNA pattern, which does not have a significant impact on Great Lakes winter climate; the positive phase of NAO is usually associated with moderate warming. When the two occurred simultaneously, the combined effects of La Niña and +NAO resulted in a negative East Pacific pattern with a negative center over Alaska/Western Canada, a positive center in the eastern North Pacific (north of Hawaii), and an enhanced positive center over the eastern and southern United States. The overall pattern prohibited the movement of the Arctic air mass into mid-latitudes and enhanced southerly flow and warm advection from the Gulf of Mexico over the eastern United States and Great Lakes region, leading to the record-breaking low ice cover. It is another climatic pattern that can induce extreme warming in the Great Lakes region in addition to strong El Niño events. A very similar event occurred in the winter of 1999/2000. This extreme warm winter and spring in 2012 had significant impacts on the physical environment, as well as counterintuitive effects on phytoplankton abundance.

Effect of the Niagara River Chippawa Grass Island Pool on Water Levels of Lakes Erie, St. Clair, and Michigan-Huron

Abstract Because of renewed riparian interest stemming from the high Lake Erie water levels of the mid-1980s and mid-1990s, and the need for a concise summary of previous studies, a review and a new assessment of the impact of the Niagara Rivers Chippawa Grass Island Pool on Lake Erie water levels was undertaken. Numerous field and modeling studies dating from 1953 through 1988 provide different assessments of the impacts. The impacts reported by the studies range from “no measureable effect” to a 2 to 5 cm Lake Erie water level decrease. The different results are due to different methods and data, and the fact that the impacts are not directly measureable. A new Great Lakes routing model that more accurately reflects the upper Niagara River hydraulics by explicitly considering the management directive of the Chippawa Grass Island Pool is used to estimate the impacts of deviating from the present directive. The long-term impact of a 0.30 m increase or decrease from the current directives long-term mean pool level on Lakes Erie, St. Clair, and Michigan-Huron levels is 5 cm, 4 cm, and 2 cm and −4 cm, −3 cm, and −2 cm, respectively. The lakes are minimally responsive to short-term changes in pool levels, with 50% of the Lake Erie impact achieved at about 6 months, and full impact achieved at about 2 years. The minimal lake response, the time lag to full impact, and the local problems resulting from directive deviations, make this a less favorable emergency response measure during periods of extreme lake levels than other alternatives.

Distributed costs of environmental contamination

Abstract Improper disposal of toxic contaminants costs society far more than just cleanup costs. Agency expenses, costs of research and litigation, and resource damages represent additional costs of pollution. These costs are generally borne by the public rather than by the polluter, and are therefore termed ‘distributed’. Two cases of PCB contamination in aquatic systems were analyzed from a distributed-costs perspective: New Bedford Harbor, MA, and the Hudson River, NY. For the cases analyzed, the major distributed cost was the loss of past and future fishery revenues. For the cases analyzed, distributed costs made up from about 40% to 99% of total costs.

Sensitivity of a sediment transport model for Lake Michigan

ABSTRACT A two-dimensional (vertical and cross-shore) sediment transport model was applied to several transects in southern Lake Michigan using observations of waves and currents recorded during the spring of 2000. Conditions during this period included several storms that are among the largest observed in the lake. The observations were used to examine the sensitivity of the model to variations in the input parameters (waves, currents, initial bottom sediment size distribution, settling velocity, and bottom stress required for erosion). The results show that changing the physical forcing (waves and currents) or the initial bottom sediment size distribution affected the results more than varying the particle properties (settling velocity and critical shear stress) or the size classes used to describe the size distribution. This indicates that for this model specification of input parameters are of first order importance and should be specified with some confidence before adding additional complexity by including processes such as flocculation and bed consolidation.